In the process for manufacturing semiconductors from single crystal silicon wafers (hereinafter, named “wafer”), various types of heat treatment are performed for the wafers by using various apparatuses. As main methods for mounting the wafers on each of the apparatuses, there are provided a first method for arranging the wafers in the apparatus in line in standing condition while supporting the periphery edge portion of each wafer and a second method for mounting the/each wafer(s) on a susceptor in the apparatus while holding the back surface side of the wafer(s). In the second method, when the heat treatment is, for example, performed for the vapor-phase epitaxial growth, a single wafer processing type, a pancake type and barrel type (or cylinder type) apparatuses are known. In the single wafer processing type apparatus, the heat treatment is performed for the wafer each time one of the wafers is mounted on the susceptor. In the pancake or barrel type apparatus, the heat treatment is simultaneously performed for a plurality of wafers arranged in line on the susceptor. In the single wafer processing type, the pancake type and the barrel type apparatuses, a circular concavity (pocket) is formed at a wafer mounting position on the susceptor. The pocket is generally made of carbon coated with silicon carbide. Diameter and depth of the pocket are designed while considering diameter and thickness of a wafer to be processed, and conditions for appropriately performing the heat treatment of the vapor-phase epitaxial growth or the like for the wafer.
In a case where the bottom of the pocket is formed on a flat surface, when a wafer W is mounted on the susceptor, the wafer easily slides on the pocket.
To prevent sliding of a wafer, grooves are, for example, cut in a lattice shape in the bottom surface portion of the pocket to form a large number of convexities formed in a trapezoid shape, as shown in FIG. 1A. Therefore, when a wafer is mounted on the bottom of the pocket, the wafer is held by the large number of convexities from the side of the back surface thereof.
In the apparatus described above, before the heat treatment, a wafer is transferred from a standby position to the susceptor, on which the heat treatment is performed, by a transfer system such as a Bernoulli-chuck transfer system or the like, and the wafer is mounted in the pocket formed in the susceptor. After the heat treatment, the wafer is transferred to the standby position to be carried out to the outside of the apparatus. This series of operations are successively performed in the apparatus. After completing the series of operations, heat treatment operations for a next unprocessed wafer are started.
Heat treatment for manufacturing a semiconductor wafer is usually performed at a high temperature atmosphere. Therefore, the pocket of the susceptor is heated to a high temperature by a high radio frequency coil, lamp or the like to heighten the wafer to a predetermined temperature.
In the apparatus described above, when the heat treatment is successively performed for the wafers, an unprocessed wafer transferred to a reaction furnace is mounted on the susceptor already heated up to a high temperature. In this case, the lower surface of the wafer is rapidly heated up at the moment when the wafer contacts with the bottom of the pocket of the susceptor. As a result, as shown in FIG. 6, the wafer is momentarily warped upward. For example, when a wafer W having a diameter of 200 mm is mounted on a susceptor 10 heated up to about 600° C., a warp momentarily occurring upward in the wafer W is observed. In this observation, a distance (amount of warp of wafer) D from one backside edge of the wafer W to the bottom of the pocket momentarily reaches about 3.2 mm.
This warp momentarily occurs in the wafer W. However, when the transfer system such as the Bernoulli-chuck is, for example, placed to be close to the wafer W, the wafer W comes in contact with the transfer system at the moment when the wafer W is warped upward, and a problem is arisen that scratches are sometimes generated on a surface of the wafer W.
An object of the present invention is to provide a method of manufacturing a semiconductor wafer and a susceptor used therefor in which warp of a single crystal silicon wafer occurring at the moment of mounting the single crystal silicon wafer on the susceptor can be lessened in the manufacturing process of the semiconductor wafer.